Add related examples

[jacobtomlinson]

Closes #107

High level changes:

• Adds a Sphinx extension that generates a mapping of tags to notebooks
• Adds a relatedexamples directive for use on pages to show related notebooks
• Added tags to the Sagemaker example notebook
• Added the related examples section to the sagemaker page
• Added ruff for linting (Split out into Add ruff to the repo linters #113)

By adding cell metadata tags to the first cell of a notebook those tags get added to the Sphinx notebook tag mapping. For example I added a cloud/aws/sagemaker tag to the Sagemaker notebook.

Then when you use the relatedexamples directive on a page it checks for any tags that match the page name. So using it in source/cloud/aws/sagemaker.md means it will find the Sagemaker notebook and link to it.

There are a few outstanding issues with the PR, but I'm keen to keep moving forwards and open separate issues to track those:

• The example link currently uses the doc name rather than the example title because Sphinx hasn't parsed the titles yet at the point I'm processing the directive Fixed in 9e37293.
• When you edit a notebook it should mark all the related pages for rebuild, but for some reason, this isn't happening

[betatim]

LGTM, modulo that one comment

[betatim]

There is no way to access the site that the CI built right? Just asking because it would be convenient but not required.

[jacobtomlinson]

Thanks for the review!

There is no way to access the site that the CI built right?

Not currently. I opened https://github.com/rapidsai/ops/issues/2413 a while back to ask Ops to set this up but they haven't gotten to it yet.